This invention relates to hydraulic clutch actuators and more particularly to hydraulic clutch actuators employing a damper mechanism.
Hydraulic actuators are known for operating a mechanism at a remote location by way of a master cylinder connected to a slave cylinder installed at the remote location. A conduit interconnects the master cylinder and the slave cylinder and the hydraulic apparatus is filled with hydraulic fluid such that, when the piston of the master cylinder is actuated, the piston of the slave cylinder and consequently the piston rod or output member is simultaneously actuated by displacement of the hydraulic fluid from the master cylinder to the slave cylinder through the conduit.
More particularly, it is known to provide such a hydraulic actuator for operating the clutch in a motor vehicle so that, when the clutch pedal of the vehicle is depressed by the driver, the slave cylinder is actuated to operate the clutch in known manner. Preferably, as described in U.S. Pat. No. 4,599,860 assigned to assignee of the present application, the clutch actuator is provided to the motor vehicle manufacturer in an assembled pre-filled form to simplify installation of the actuator on the vehicle, avoid the inconvenience of potential spillage of hydraulic fluid during on-line filling, eliminate the necessity to bleed or purge the lines of the actuator to facilitate the filling process, and eliminate the need to test the actuator after installation and filling. Whereas hydraulic clutch actuators, and particularly prefilled clutch actuators, have enjoyed significant commercial success, they have the ability to transmit vibrations backwardly through the system from the clutch through the clutch pedal with the result that the operator may experience unpleasant vibrations at the clutch pedal.
Specifically, imbalances in the crank shaft of the vehicle engine or engine firing impulses are transmitted to the flywheel which under goes a swashing movement, the flywheel swashing movement in turn leads to vibrations of the spring fingers of the clutch release mechanism, the vibrations of the spring fingers are transferred to the release bearing of the clutch, and the vibrations propagate backwardly through the hydraulic fluid in the slave cylinder, through the hydraulic fluid in the conduit interconnecting slave cylinder and the master cylinder, through the hydraulic fluid in the master cylinder, and then through the master cylinder push rod to the clutch pedal where they are experienced by the operator as vibrations of the clutch pedal. The propagated vibrations may also generate a pedal growl which is audible to the operator as well as a clutch roar which also may be audible to the operator.
Various devices have been proposed in an attempt to attenuate these vibrations. For example, tuned masses have been attached to various parts of the clutch system including the clutch release lever, the slave cylinder push rod, and the clutch pedal; rubber dampers have been employed in the master cylinder push rod; rubber hose sections have been employed in the conduit interconnecting the master cylinder and the slave cylinder; and various damper devices have been proposed for installation in the interconnecting conduit. In particular, a damper device as shown in British Patent Specification 1562709 or as shown in U.S. Pat. Nos. 4,998,609 or 5,320,203, all assigned to the assignee of the present invention, may be installed in the conduit interconnecting the master cylinder and the slave cylinder.
Whereas these prior art devices have been successful in varying degrees in attenuating the vibrations in the system, they are dedicated to attenuating vibrations in a predetermined frequency range and accordingly are ineffective in attenuating vibrations falling outside of the predetermined range. Specifically, damping devices that are effective in attenuating the high frequency vibrations occurring in the system during engagement and disengagement of the clutch during normal driving are generally ineffective in attenuating the low frequency vibrations appearing at the clutch pedal during engine idle conditions with the transmission in neutral.
This invention is directed to the provision of an improved damper device for use in association with a hydraulic clutch actuator.
More particularly, this invention is directed to the provision of an improved damper device for use in association with a hydraulic clutch actuator which effectively attenuates various frequency vibration ranges in the system.
This invention relates to a damper for provision in a hydraulic actuator system between a master cylinder and slave cylinder of the system. The damper includes a housing, including port means for connection in the system, and an imperforate diaphragm carried by the housing beneath the port means and forming a boundary wall of the system so that the diaphragm may deflect in response to vibrations transmitted through the hydraulic fluid in the system to effect damping of the vibrations.
According to the invention, the housing has a canister configuration and includes a thin imperforate annular sidewall above the diaphragm of substantially uniform thickness and coacting with the diaphragm to define a large volume chamber above the diaphragm providing further system damping by virtue of vibratory volumetric expansion of the annular sidewall. This arrangement allows the diaphragm to attenuate low frequency vibrations while allowing the vibratorily expanding annular sidewall to attenuate relatively high frequency vibrations.
According to a further feature of the invention, the imperforate diaphragm comprises an elastomeric diaphragm and the damper further includes a relatively stiff diaphragm positioned beneath and generally parallel to the elastomeric diaphragm to form a gas chamber therebetween and forming a back up for the elastomeric diaphragm. With this arrangement, the elastomeric diaphragm may deform against the relatively stiff diaphragm in response to intermediate frequency vibrations transmitted through the hydraulic fluid to cause deflection of the relatively stiff diaphragm and effect damping of the intermediate frequency vibrations.
According to a further feature of the invention, the volume of the hydraulic chamber substantially exceeds the volume of the gas chamber whereby to provide a large volume chamber effective to damp the high frequency vibrations in the system.
According to a further feature of the invention, the housing includes an upper part defining the annular sidewall and the port means and a lower part positioned beneath the stiff diaphragm and the upper and lower parts coact to clamp peripheral edge portions of the elastomeric diaphragm and the stiff diaphragm therebetween. This arrangement provides a convenient packaging means to provide a damper able to attenuate low frequency, intermediate frequency, and high frequency vibrations in the system.
According to a further feature of the invention, the annular sidewall is configured above the elastomeric diaphragm to have a domed configuration with the port means substantially at the apex of the dome. The domed configuration above the elastomeric diaphragm facilitates the vibratory volumetric expansion of the fluid chamber.
According to a further feature of the invention, the elastomeric diaphragm comprises a rubber diaphragm; the housing is formed of a plastics material; and the stiff diaphragm comprises a spring steel diaphragm.
Other objects and advantages and applications of the present invention will become apparent to those skilled in the art when the following description of the best modes contemplated for practicing the invention are ready in conjunction with the accompanying drawings.
Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.